1. Field of the Invention
This invention relates to harmonic drive mechanisms, and more particularly to flexspline support arrangements in harmonic drive transmissions.
2. Prior Art
Harmonic drive transmissions were originally called "strain wave gearing" and were initially introduced by Musser in U.S. Pat. No. 2,906,143. Such original harmonic drive transmissions or strain wave gearing comprised a rigid circular spline having "N" teeth, a flexspline having fewer than "N" teeth ("N" being a positive integer) and being disposed within the circular spline, and a rotatable wave generator disposed in the flexspline to deform the flexspline into a lobed configuration, such as an oval shape, so as to force the flexspline into engagement with the circular spline at two points on the major axis of the formed ovaloid.
The wave generator may include an oval cam plate and a bearing snugly mounted on the outer periphery of the cam plate. The outer bearing is matingly inserted into the flexspline so as to deform it to the peripheral contour of the cam plate. An input shaft attached to the cam plate provides rotation thereto, causing the ovaloid configuration of the flexspline to be correspondingly rotated. During such rotation, the circular spline is induced to rotate, relative to the flexspline, in an amount proportional to the difference in the number of teeth between the flexspline and the circular spline. When an output shaft is arranged on either the flexspline or the circular spline, that output shaft is rotated very slowly in comparison to its input shaft. Such harmonic drive, strain wave gearing has been utilized in machinery requiring a high reduction ratio.
The flexsplines are generally cup-shaped, having an open first end and a closed second end. The closed second end usually comprises a diaphragm having a central, generally circular boss thereon. The boss comprises a thickened portion of the diaphragm, as may be seen in U.S. Pat. No. 5,269,202 to Kiyosawa et al. The diaphragm radially outwardly of the boss disclosed in this patent decreases in thickness as it extends radially outwardly from that boss. This flexspline would be bolted to a hub for transmission of rotary motion therebetween. The deflection of the diaphragm as represented by this patent is more towards the mid-portion of that diaphragm, thereby resulting in a less stiff diaphragm than desired, at the teeth of the cup.
It is an object of the present invention to provide a flexspline having improved diaphragm support, to provide improved stiffness at the teeth of the cup.
It is a further object of the present invention to provide a flexspline which overcomes the disadvantages of the prior art.
It is still yet a further object of the present invention to provide a diaphragm which deflects principally at the corner of the cup, and less at a mid-portion of the diaphragm.
It is yet a further object of the present invention to provide a flexspline having a higher load capacity by virtue of its support arrangement.